Recently, a lithium secondary battery applies to transportation application field such as Hybrid Electric Vehicle HEV, Plug-in Hybrid Electric Vehicle PHEV and Electric Vehicle EV, and high electric power consumption field such as Smart Grid application electric power storage.
According to such tendency, it is promoted to change the electrode material, enhance the coating technology, enhance the packing technology and enhance the lithium absorption rate in cathode, in order to enhance energy density of the secondary battery. However, means except for the change of the electrode material has been developed by the optimized internal space and design in the art, and it is currently known that the means reached the limit.
Recently, a research is being carried out to use Si series alloy and Sn series alloy as the anode active material in order to enhance the energy density of the lithium secondary battery. When the Si series is used as a cathode material, it may be expected to obtain the theoretical capacity (4010 Ah/Kg) which is 10 times the theoretical capacity of Graphite (372 Ah/Kg), so that it is considerably excellent in the energy density.
However, while the theoretical volume change rate of graphite is 12%, that of silicon is 300% to 400%, which is 20 times or more. Therefore, in case that Si series alloy is used as the anode active material, particles gradually come out due to the expansion of the alloy by the volume change in the procedure that the lithium ion comes into and out of the cathode material while charging and discharging repeatedly, so that there occurs a drawback in that the cycle characteristic is declined. When the volume change of an active material is great, there occur a crack of the active material particle and a loose contact between the active material and a current collector so that there also occurs a problem that the life of charging and discharging cycle becomes shortened.
Especially, when there occurs a crack in the active material particle, since surface area of the active material particle becomes increased, the reaction between the active material particle and a non-aqueous electrolyte becomes increased, whereby a film composed of decomposition product of the non-aqueous electrolyte is easily formed on the surface of the active material. When such a film is formed, an interfacial resistance between the active material and the non-aqueous electrolyte becomes increased, causing the life of the charging and discharging cycle to be shortened. In order to solve such a problem, a composition of the material used as the anode active material should be uniformly formed.
The anode active material of Si series may be manufactured using the melt spinning method, and a conceptual view for a manufacturing apparatus employing the melt spinning method is illustrated in FIG. 1. The manufacturing apparatus employing the melt spinning method includes a crucible 501 to melt and contain an alloy of a raw material, and a rotation roller 503 which contacts a molten alloy 502 discharged from the crucible 501. The molten alloy 502 discharged from the crucible 501 is cooled in contact with the rotation roller 503, and the product thereof is formed in a ribbon type.
In case of such a manufacturing apparatus, however, when the molten raw material is wholly exhausted, there is needed an additional work for exchanging, such as opening a sealed apparatus in order to replenish the raw material again, so that the work continuity is declined. Further, the total process is delayed since the raw material supplied again should be melted.